The present invention relates to the field of RF power amplifier technology, specifically to the power combining method and the power-combiner circuit for a RF power amplifier.
The RF power amplifier (PA) is an important part of the wireless communication system. PA, used for the final stage of the transmitter, amplifies the modulated band signal to the required power value and passes it to the antenna for transmission. A communication system often works in multiple frequency bands, which requires a system of multi-channel switches to realize independent working of different bands. However, there is usually only one antenna equipped on the handheld device for the sake of smaller volume and increased portability, so the RF power amplifier power combiner circuit shall control between the RF power amplifier and the antenna. Therefore, the performance of RF power amplifier power-combiner circuit in such things as power capacity, insertion loss, isolation, and anti-voltage breakdown ability will greatly affect the performance of the entire wireless communication system. And these performance indicators also impose tough requirements on the RF power amplifier power combiner circuit components such as switches and duplexers. To meet the high requirements of the RF power amplifier, expensive GaAs technology is adopted for the design of most power-combiner circuit switches, the disadvantages of which include not only complicated circuit design, but also high cost, low integration and immature process compared to common CMOS technology.
At present, traditional power-combiner circuits for RF power amplifiers are generally as shown in FIG. 1. The overall circuit includes switches SW1, SW2, matching network, matching network D, the RX receiver port, duplexers, antennas and the ESD circuit on the antenna side. As the bridge between the RF power amplifier and antenna, switches SW1 and SW2 should have a high breakdown voltage, and can withstand the high-power signal launched by the RF power amplifier to prevent collapse of the entire communication system caused by switch damage. And for the whole RF power amplifier power combiner circuit, its isolation degree will also affect the overall system performance. As shown in FIG. 1, when Band1 channel of the PA transmits power, the PA output power is transmitted to the antenna through switch SW1 and the duplexer. Since switch SW1 must bear all of the PA transmit power, it must have a high breakdown voltage and over-power capability, which means only expensive GaAs technology with high breakdown voltage is available to make the switch, and the insertion loss of the switch cascaded in the emission path will directly impact the power of the antenna side; when RX side receives power, the signals at the antenna end reach the receiver through the duplexer and SW5-SW8, and the receiver insertion loss of switch SW5-SW8 cascaded in the receiving path will directly affect receiver sensitivity of the entire communication system. In summary, the RF power amplifier power-combiner circuit and its switches and key components require very high over-power capability, very low insertion loss to reduce the output RF signal attenuation. And high isolation degree of the combiner circuit is also required to reduce signal leakage between power channels. Traditional switches in the RF power amplifier power-combiner circuit are mostly designed with PHEMT tubes using expensive GaAs technology to meet the requirements of low insertion loss, high isolation degree, high over-power capability and high breakdown voltage. However, the PHEMT tube is a depletion-mode FET, and drives the gate with negative voltage, which increases design complexity and the cost of design and production of the switch control circuit. While designing switches with the CMOS technology has the advantages of high integration, technical maturity and low cost, it also has the disadvantes of low breakdown voltage, and a limited switch isolation degree. Thus, it is crucial to design a low-cost, high-performance RF power combiner network from the view of overall network of the RF power amplifier power combiner circuit and in combination with the advantages of CMOS technology.